Interfacing MaxII Micro to 5v TTL

[Altera_Forum]

Hello, 

I got myself a Max Micro kit, and I'm planning to interface this with a 5v TTL device. But I'm not sure if I\O pins are 5v tolerant. What can I do to interface a max micro to 5v TTL devices ? I know I have to use pull up/pull down resistors, but what should be the values ? Unfortunately I don't have any electric background :(. Any help or pointers highly appreciated.  The CPLD on my Max Micro is EPM2210F324C3N.  thanks !

[Altera_Forum]

hello coze,I just saw your posting, and I'm new to MaxIImicro kit. did you solve the problem? I wonder if you connect 5VTTL. 

I just started with MaxIImicro, what I do is just download demo .pof files to chip and run not more.

[Altera_Forum]

Use a transistor supplied at +5V if you need to increase the voltage from 3.3V to +5V and use a resistor partition scheme (e.g. 560ohm and 1kohm) if you need to decrease a signal from 5V to 3.3V. 

;)

[Altera_Forum]

...or you could use an external buffer device... 

 Something like a 74LVT245  http://www.fairchildsemi.com/pf/74/74lvt245.html  3.3V but 5V tolerant. Guess it depends on how many IOs etc you have on your interface and what the fan out is etc  Rgds

[Altera_Forum]

The Max II handbook is giving detailed answers to all questions raised here. There is particularly a paragraph titled multivolt i/o interface. 

 1. Max II clearly isn't 5 V tolerant. 2. TTL inputs can be driven from MAX II banks with VCCIO of 3.3V (3.3V LVCMOS I/O standard) without level translation. 5V CMOS logic needs level translation, cause minimum Vih can't guaranteed. 3. To drive MAX II from 5V-logic, you can use voltage dividers, series resistors with clamp diodes (for some MAX II inputs, internal pci clamp diodes can be activated) or level translation.

[Altera_Forum]

Yes to interface to 5v you will need some kind of level shifter, 

a part such as 74LVC8T245 is easy to use and can be used in both directions. If you just need to drive 3.3V to 5V then in non critical applications then you can use a 74ACT241 and supply the 74ACT241 with 5V. Going from 5V to 3.3V you can use the  74LVC244 and supply at 3.3V   Regards   Uk Fixer